1. Field of the Invention
The invention is directed to sunscreen compositions, and in particular, sunscreen compositions, products and methods having polymeric additives that improve water resistance of UVA actives contained therein.
2. Description of Related Art
Numerous sunscreens are currently available for protecting keratinous substrates such as skin and hair from ultraviolet (UV) solar radiation falling within both the UVB region (between 290 nm to 320 nm wavelengths) and the UVA region (between 320 nm and 400 nm wavelengths). Protection from UVA radiation is measured as a Protection Factor-UVA or PFA. Protection from UVB radiation is measured as a Sun Protection Factor or SPF. For instance, UVB radiation is absorbed by the epidermis layer causing erythema and cellular mutations, all of which damage the skin and underlying tissue. UVA radiation is even more damaging as it reaches deeper into the dermis layer. As such, UVA radiation may suppress immune functions, lead to loss of skin elasticity, promote premature signs of aging, as well as other undesirable health effects.
Currently available sunscreens can protect against both UVB and UVA radiation. However, water exposure and other adverse conditions such as sweat, can lead to diminished protection as the sunscreen can wash off the skin. Sunscreen manufacturers provide the consumer with a water resistance rating that is dictated by the 2011 U.S. Food & Drug Administration (FDA) Final Rule for Water Resistance wherein a sunscreen composition must meet the critical wavelength of 370 nm. However, the critical wavelength protocol does not take into account the efficacy of the sunscreen composition after exposure to real life conditions of water, sweat, salt water or pool water. Under the adverse conditions of water, salt, and/or chemicals, the sunscreen composition can lose its efficacy and provide limited or no protection to the consumer. Yet even though the critical wavelength is met, SPF is primarily a measure of protection against UVB radiation only. As such, a loss in protection against UVA radiation after a period of water immersion is not accounted for in efficacy testing.
The SPF of a sunscreen composition is determined by measuring the minimal erythema response on human skin treated with a sunscreen composition and untreated human skin on a single human subject. From these two measurements, the SPF is the ratio of the energy required to generate erythema on treated skin as compared to the energy required to generate erythema on untreated skin. While erythema is produced on human skin exposed to both UVB and UVA rays, UVB rays play a much greater role in their effect on skin. The erythemal action spectrum reveals that 99% of erythemal action resides in the UVB region and only 1% in the UVA region.
The marker used to measure UVA Protection Factor (UVAPF) is referred to as Persistent Pigment Darkening (PPD), which implements use of UVA rays only. PPD is based on the skin's response to the amount of UVA that enters the viable epidermis. One such test measures sunscreen-protected PPD skin to the unprotected PPD skin after exposure to UVA. However, these tests do not measure water resistance of UVA sunscreens.
Again, whether or not a sunscreen is deemed water resistant is based on the 2011 FDA Final Rule for water resistance. By relying on testing in which 99% of the effective energy dosage comes from UVB rays, and only 1% coming from UVA rays, currently available sunscreens incorrectly imply that both UVB and UVA protectants are “water resistant” to the same degree. As such, loss in protection against UVA radiation after a period of water immersion is not accounted for in sunscreens.
To overcome these deficiencies in the prior art, the present invention provides products, methods and sunscreen compositions with an increase in water resistance, namely, an increase in the water resistance of the UVA sunscreen active agents.